1. Field of the Invention
The invention relates to an apparatus useful for performing fractional distillation or other forms of vapor-liquid contacting. The invention more specifically relates to a process and apparatus providing a high capacity and high efficiency cocurrent flow fractionation apparatus useful in fractional distillation columns to separate volatile chemicals such as hydrocarbons.
2. Related Art
Fractional distillation has traditionally been conducted in counter current contacting devices having an overall downward liquid flow and upward vapor flow. At some point in the apparatus the vapor and liquid phases are brought into contact to allow the vapor and liquid phases to exchange components and approach equilibrium with each other. The vapor and liquid are then separated, moved in the appropriate direction and contacted again with another quantity of the appropriate fluid. Except for in a few exceptions such as noted below, in the traditional stage contacting vapor and liquid are contacted in a cross flow arrangement at each stage. The subject apparatus differs from traditional multi-stage contacting systems in that while the overall flow in the apparatus continues to be countercurrent, each stage of actual contacting between the liquid and vapor phases is performed in a cocurrent mass transfer zone.
Cocurrent vapor-liquid contacting devices are described in the patent literature. For instance, U.S. Pat. No. 4,752,307 issued to G. Asmus et al. and U.S. Pat. No. 5,885,488 to G. Konijn present devices in which rising gas lifts liquid into a cocurrent contacting zone. A swirl imparting means helps separate the two phases after contacting. U.S. Pat. No. 5,683,629 issued to G. Konijn also describes a fractionation tray in which the vapor passes upward through a swirl imparting means cocurrent to liquid.
U.S. Pat. No. 4,361,469 issued to W. R. Trutna also presents an apparatus for use in fractionation or absorption in which cocurrent vapor and liquid flow is used in the contacting step. The apparatus employs tray-like devices to intermix the liquid into rising vapor, with downcomers at the edge of the trays carrying the liquid downward from separators located over the trays.
U.S. Pat. No. 5,690,708 issued to A. Danckaarts et al. describes a fractionation tray in which the vapor enters a contacting section horizontally through porous walls and then passes upward with entrained liquid into a separation section.
U.S. Pat. No. 5,798,086 issued to D. C. Erickson presents a fractionation tray having adjacent cocurrent risers and downcomers spread across the tray.
U.S. Pat. No. 5,837,105 and related U.S. Pat. No. 6,059,934 issued to B. K. Stober et al. disclose a fractionation tray having multiple cocurrent contacting sections spread across the tray. Liquid emanating from a central downcomer is entrained in vapor rising through vapor openings and passed into one of two de-entrainment devices. The liquid from two de-entrainment devices then flows into a downcomer.
The invention is a novel high capacity and high efficiency vapor-liquid contacting apparatus for use in fractionation columns. The apparatus is characterized by a modular rather than tray-like construction, with the symmetrical modules interlocking to form two cocurrent vapor-liquid riser channels which carry fluid up to one of the two vapor-liquid separators of each module. These separators partition the vapor and liquid such that the vapor and liquid can separately flow upward and downward respectively after being contacted. The liquid flows into a V-shaped downcomer, with one wall of the downcomer also forming a wall of the cocurrent vapor-liquid flow channel. Variations relate to the design of the separators, channels and overall apparatus.
One broad embodiment of the invention may be characterized as a vapor-liquid contacting apparatus useful for performing fractional distillation of a multi-component feed stream, which apparatus comprises an apparatus for performing vapor-liquid contacting, including fractional distillation of a multi-component feed stream, which apparatus comprises an external, substantially enclosed, vertical outer vessel; a plurality of contacting modules adapted to be placed in layers in the vessel, with each module having an upper end and a lower end and comprising a tapered downcomer located at the lower end of the module and formed from two opposing inclined walls, the downcomer having a liquid outlet opening at its lower end and an inlet opening at its upper end; horizontal extension plates projecting outward from the upper end of each opposing wall; a pair of vapor-liquid separation chambers located at the upper end of each module with one chamber being located above each of the horizontal extension plates, with the chambers being spaced apart on opposite sides of the module to form an intermediate fluid transfer volume located above and communicating with the inlet opening of the downcomer, and with each of the chambers having an outlet surface facing the fluid transfer volume and an opposing inlet surface; and, substantially imperforate walls extending upward from the horizontal extension plates to the vapor-liquid separation chambers; with the modules being stacked in horizontal layers having the modules spaced apart horizontally, and with the downcomers of each upper layer of modules extending downward into a space between two adjacent modules of a lower level of modules to define two vapor-liquid contact channels leading to the inlet surface of the separation chambers of the upper layer of modules.